Research from previous cycles of this P01 has focused on the role of phonology in word level reading, speech perception, speech production and the relaflonship between each of these systems. Project IV seeks to extend upon this work by looking at the cognitive and neurobiological processes that contribute to individual differences in comprehension of spoken and written language. A signiflcant number children have substanflal problems with comprehension, despite adequate word level decoding ability and sub- lexical phonological processing (Nation, 2005). If decoding and subword-level phonological processing are not the botfleneck leading to poor comprehension ability, other mechanisms must be responsible. We propose that weakness in comprehension is due to language speciflc deflcits in relevant sub-skills such as semanflc and syntactic processing, and that individual differences in these skills will be largely common to both printed and spoken language. Our theoretical approach is informed by the lexical quality hypothesis, LQH (Perfetti, 2005) which posits that pooriy specifled word representaflons at any level (orthography, phonology, semanflcs) will lead to poor lexical quality (in both spoken and written domains): in line with the LQH we propose that poor lexical quality that results from underspecifled semantic relationships is the primary lexical level constraint on comprehension skill. Moreover, we propose that this extends to relaflonal semantic and syntactic knowledge (understanding how words and concepts within a text are related) and that this skill is the bridge between lexical and sentence/discourse level skill. The broad goals of Project IV are to (in a populaflon of high school students): a) identify the common and disflnct neural systems and behavioral proflles that support successful comprehension in the visual and spoken domains, b) investigate aspects of word level semanflcs across both the spoken and written domains and how the quality of this word-level knowledge impacts the ability to compose words into larger phrasal or sentence-level constituents and c) examine the role of learning and plasflcity to overall comprehension ability and d) investigate areas of phonological processing which have previously been under explored in relation to comprehension skill: namely, prosody. RELEVANCE (See instructions): This program is relevant to the understanding the development of spoken and written language competence which is crucial for successful academic and life outcomes. By examining the underlying cogniflve and neural bases of both spoken and printed comprehension problems in high school aged children (without problems in word reading or phonological processing). Project IV contributes signiflcanfly to the